At liberty to do something

Pro Tip 1/3

Use it when you've got explicit permission, not just because there's no rule against it.

I'm at liberty to use the car since Mom said I could.

Pro Tip 2/3

It suggests a choice, meaning you're not obliged or expected to do something.

You're at liberty to leave the event early if you want.

Pro Tip 3/3

It's more formal and may sound outdated in casual conversations. Use it in writing or formal speech.

You are at liberty to submit your complaint in writing.